1. Field of the Invention
The present invention pertains to porous media type air filter units with multiple jet reverse flow cleaning systems for the filter elements wherein a substantial volume of jet cleaning air and entrained ambient air is used to flush the filter elements to remove accumulated dust particles.
2. Description of the Prior Art
The configuration of conventional air filter elements, being a substantially cylindrical annular pleated paper or cloth bag type structure, has resulted in the development of reverse air flow cleaning systems wherein a single jet nozzle is disposed in or somewhat downstream of the inner clean air chamber defined by the filter element and aimed in the opposite direction to that of the clean air flow through the filter element itself.
In one type of system, the jet nozzle is typically adapted to provide a short burst or pulse of pressure air in the range of 80-100 psig for short duration to create a pressure wave which flows through a reduced throat flow venturi and into the bore of the filter element in reverse direction to remove the dust which has accumulated on the surface of the element itself.
However, with high pressure air pulse type reverse flow cleaning systems a relatively inefficient process is carried out and the reverse flow pressure wave unduly stresses the filter media. In order to overcome the problems with such prior art systems certain types of barrier filter elements such as the porous media pleated paper type have been grossly derated as to their filtering capacity to prevent early filter element deterioration and failure due to the reverse pulse jet action. Derating of the element for one such pulse jet system is to a maximum capacity of 1-3 cubic feet per minute of filter air flow per square foot of filter surface area.
In another type of system in the field of self-cleaning air filtration systems, more efficient filter cleaning is accomplished by a reverse air flushing system that is adapted to produce a jet of air discharged from a compressed air reservoir through a quick opening air valve at about 40 to 60 psig. The quick opening air valves operating at this pressure commonly range in discharge orifice size from 3/4 inch up to about 2 inches and this means of cleaning permits filter media flow capacities of about 3-5 cubic feet per minute. The discharge orifice of the valve is placed directly over a discharge flow tube placed over the discharge bore of the cylindrical filter and the valve is positioned at a height above the flow tube to allow the air jet emitted by the quick opening valve to expand to strike the bore wall of the tube. The bore of the flow tube may be of lesser or equal size of the filter bore for the purpose of receiving the reverse flushing jet. The jet strikes the wall of the flow tube bore to effect a pressure seal and to provide an eductor effect to draw additional air into the filter bore. The pressure seal effect causes the air to be forced through the filter media to remove the dust cake.
In order for the heretofore existing reverse flushing systems to operate properly, the system designer must plan the relationship of the flushing jet diameter to the flow tube bore diameter so that a proper point of intersection is achieved. Typically, the quick opening valve emits a jet that expands in a cone having a 15 degree to 20 degree included angle and the jet spacing with respect to the flow tube bore is adjusted accordingly Obviously, the larger the filter bore, and thus the flow tube bore, the further the quick opening valve discharge outlet must be placed from the flow tube bore opening. The greater the distance at which the valve is placed from the tube bore opening, the larger the cabinetry becomes that houses the reverse flushing system.
In co-pending U.S. patent application Ser. No. 549,963, filed Nov. 7, 1983, now U.S. Pat. No. 4,544,389, there is disclosed a multiple orificed air jetting device that is attached to a quick opening air discharge valve. This multiple orifice device diffuses a single concentrated air stream into a number of jetting air streams over a larger surface area. Thus, in the case of a round bore filter, the multiple orifices are placed in circular form relative to the flow tube and filter bore size. The flushing system may thus be placed in close proximity to the flow tube bore opening and, accordingly, reduces the height of the cabinetry housing the flushing system.
While the multiple orifice device of co-pending Application Ser. No. 549,963, now U.S. Pat. No. 4,544,389, is extremely effective as a filter reverse flushing system, it tends to generate an energy loss in the compressed air stream between the quick opening valve and the discharge orifices. A loss is encountered as the air stream expands into the multiple orifice supply chamber and is again compressed into the individual orifices. In other words, the velocity of the air stream emitted from the single orifice of the quick opening valve is slowed and then reaccelerated through the orifices.
Additionally, the cabinetry enclosing the multiple orifice filter reverse flushing system can now be reduced to the point that installation of quick opening air discharge valves may be difficult. Presently existing quick opening valves are provided with threaded pipe connections to a pressure fluid supply. Additionally and more importantly, the cabinetry clearance required to rotate the valve as it is being assembled to the supply connection often compromises the potential size reduction of the cabinetry that the multiple orifice device affords.
The aforementioned problem in the art of porous media air filter reverse air cleaning with single jet quick opening air valves and with multiple jet openings in combination with existing single port discharge quick opening air valves, has led to the development of the present invention.